<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
       div{
            width: 100px;
            height: 100px;
            background-color: pink;
        } 
        .new {
            position: absolute;
            width: 200px;
            height: 200px;
            left: 200px;
            top: 200px;
        }       
    </style>
</head>
<body>
    <script src="js/common.js"></script>
    <input type="button" value="按钮" id="btn">
    <div id="box"></div> 
    <script>
        var btn = my$("btn");
        var box = my$("box")
        btn.onclick=function(){
            // box.className = "new";
            box.style.width="200px";
            box.style.height="200px";
            box.style.top="200px";
            box.style.left="200px";
            box.style.position="absolute";

        }
        
    </script>   
</body>
</html>